Flexible cord-like hollow object

ABSTRACT

The invention pertains to a flexible cord-like hollow object with an inner zone, which is enclosed by a casing, for the transportation of media, whereby a barrier layer ( 26 ), which is impermeable to the volatile molecules of the medium that is to be transported, is integrated into the casing ( 12 ).  
     The feature is provided that the barrier layer ( 26 ) comprises sub-elements ( 30 ) that are arranged in a scale-like manner.

[0001] The invention pertains to a flexible cord-like hollow object withan inner zone, which is enclosed by a casing, for the transportation ofmedia.

[0002] Flexible cord-like hollow objects of this generic type are known.These cord-like hollow objects, which are also called tube[s] below, areused in many sectors of industry for the transportation of liquid orgaseous media. Such tubes are used for the transportation ofrefrigerants for use in technical climate control units, e.g. in motorvehicles. Refrigerants have the property that they are volatile and leadto harmful effects when they get into the earth's atmosphere. In orderto avoid this, use should be made of natural refrigerants, e.g. CO₂. Inthe case of known refrigerant tubes, it is a disadvantage that these arenot diffusion-proof and that they exhibit high permeability to naturalrefrigerants, especially carbon dioxide CO₂.

[0003] A flexible pipe for the transportation of media is known from EP0 375 608 A1 in which a barrier layer is integrated into the casing of aflexible cord-like hollow object in order to reduce permeation.

[0004] The barrier layer is formed from a longitudinal or spiral-shapedmetal foil that is overlapped at the edges of the strip. In the case ofthis arrangement, it is a disadvantage that freedom from leakage of thebarrier layer cannot be ensured adequately especially in the event of ahigh bending stress.

[0005] Thus the objective of the invention is to create a flexiblecord-like hollow object of this generic type that has low permeabilityin combination with high flexibility, especially in the case of CO₂.

[0006] In accordance with the invention, this objective is accomplishedby means of a flexible cord-like hollow object with the characterizingfeatures that are designated in claim 1. As a result of the feature thata barrier layer, which is impermeable to the volatile molecules of themedium that is to be transported, is integrated into the casing of thehollow object and that the barrier layer comprises sub-elements that arearranged in a scale-like manner, permeation through the flexiblecord-like hollow object is prevented with high efficiency or it is atleast reduced to a negligibly low value. Thus it becomes possible totransport refrigerants without the volatile components of therefrigerant being able to get into the atmosphere, especially when, asis preferred, the flexible cord-like hollow objects are used as arefrigerant tube. A low rate of permeation simultaneously ensuresreliable functioning of the refrigeration unit that is to be suppliedwith the refrigerant. In particular, the scale-like arrangement of thesub-elements permits stressing due to bending of the flexible hollowobject as previously. Because of the overlapping of the sub-elements,this freedom from leakage of the barrier layer is not impaired duringstressing due to bending. The scale-like arrangement of the sub-elementsleads to the situation in which the barrier layer does not break duringstressing due to bending. Breakage or damage to the barrier layer wouldlead to an increase in the rate of permeation.

[0007] The scale-like construction can be achieved in a veryadvantageous manner by producing an appropriate crystal structure duringthe vapor deposition of the metallic barrier layer that is preferablyprovided.

[0008] The scale-like construction for the crystal structure canpreferably be obtained via the vapor deposition of a crystallinesubstance on a layer of the casing that serves as a carrier layer,whereby the crystalline substance comprises e.g. metal or a syntheticmaterial. As a result, crystalline regions (platelets) are produced,which are absolutely impermeable, on the surface of the layer of thecasing that serves as the carrier. As a result, the situation is reachedin the non-expanded state, i.e. the non-stressed state, that theflexible cord-like hollow object (tube) is almost completely impermeableto the refrigerant that is to be transported. Negligibly low permeationcan arise only through extremely small seams between the vapor depositedplatelets. If the platelets are vapor deposited in such a way that theyoverlap, then a degree of overlapping of the platelets can be ensuredeven during stressing due to bending or tensile stressing of the tube sothat, for example, 99% of the total surface is covered with thecrystalline platelets even in such a state of the tube.

[0009] An advantageous feature, in particular, as a result of this isthat use can be made of the flexible cord-like hollow object, which hasbeen provided with the crystalline platelets, even in the high pressurerange and the low permeability remains intact. Such high pressureexpansion tubes, which have been provided with such a barrier layer inaccordance with the invention, excel by virtue of their highflexibility, shrinkage attenuation and favorable effect on acoustics sothat these advantages can be exploited along with the simultaneousassurance of low permeability.

[0010] In particular, use can be made of carbon dioxide CO₂ as therefrigerant in high pressure expansion tubes that have the barrier layerin accordance with the invention. The use of carbon dioxide as therefrigerant in the high pressure range leads, as such, to the problem ofso-called decompressive explosion in the event of a sudden drop inpressure. The formation of large aggregates of the refrigerant occursabruptly in a material that is in contact with the refrigerant. Thiswould lead to damage or, as the case may be, the destruction of thematerial. As a result of the barrier layer in accordance with theinvention, the situation is now reached in which damage to the material,i.e. the casing of the flexible cord-like hollow object here, cannotoccur since permeation of the molecules of carbon dioxide, which is usedas the refrigerant, into the casing is prevented.

[0011] Permeation is prevented or, as the case may be, reduced to anegligible minimum even in the case of high pressure expansion becauseof the aforementioned scale-like arrangement of the crystallineplatelets in particular.

[0012] Moreover, it is preferable if the barrier layer comprisessub-elements that have been arranged in a scale-like manner, whereby thesub-elements overlap in the longitudinal extension of the hollow objectand/or coaxially relative to a longitudinal axis of the hollow object.As a result, a leakage-proof arrangement of the barrier layer isachieved that, moreover, impairs the flexibility of the hollow objectonly to an insignificant extent.

[0013] In a preferred form of embodiment of the invention, the featureis provided that the barrier layer is arranged on the outer casingsurface of an inner layer of the casing. As a result, it becomespossible and preferable to integrate the barrier layer into the casingwithout this [casing] impeding the cross section of the inner zone ofthe hollow object. The inner casing surface of the inner layer of thecasing can thus be optimized in terms of the medium that is to betransported so that flow resistance, which is as low as possible, isprovided. However, the barrier layer, which is applied to the outercasing surface of the inner layer, prevents the diffusion of thevolatile components of the medium, which is to be transported, throughthe casing. In the event that these diffuse through the inner layer ofthe casing, they then encounter the barrier layer and they cannot passthrough the casing. Thus the low permeability of the casing is ensured.

[0014] In a further preferred form of embodiment of the invention, thefeature is provided that the barrier layer comprises metal or asynthetic material. As a result, a material can be selected in a simplemanner that is optimal for the medium that is to be transported, wherebythe material exhibits especially good barrier action with respect to thevolatile components of the medium that is to be transported.

[0015] Moreover, the feature is provided in a further preferred form ofembodiment of the invention that the barrier layer is connected to theouter casing surface of the inner layer of the casing in a non-positive[adherent] manner. As a result, the situation is reached in whichdetachment of the barrier layer can be prevented during subsequent usageof the flexible cord-like hollow object in accordance with directions sothat the low permeability, which has been achieved, remains intact. Thefeature is preferably provided that the casing surface is treatedphysically and/or chemically in order to increase the strength ofadhesion between the barrier layer and the casing surface. As a result,roughening can be achieved, preferably and in particular, and thisensures better adherent bonding to the subsequently applied barrierlayer.

[0016] In particular, it is preferred that an increase in the strengthof adhesion between the barrier layer and the casing surface be obtainedvia the polarization or activation of the material of the casing atleast in the surface region of the casing surface of the inner layer ofthe casing. Depending on the material of the casing, which preferablycomprises a polymer, polar groups can be incorporated, as a result, intothe basic molecular structure of the casing, whereby these polar groupsensure an improvement in the coating of the casing surface with thebarrier layer.

[0017] In a preferred form of embodiment of the invention, moreover, thesituation is provided in which an additional bonding agent is arrangedbetween the barrier layer and the casing surface. This additionalbonding agent leads to an especially strong and durable non-positive[adherent] joint between the barrier layer and the casing so that theadherent bonding between the barrier layer and the casing remains intacteven with relatively intense mechanical stressing during usage, which isin accordance with directions, and its low permeability can bemaintained.

[0018] Further preferred forms of embodiment of the invention resultfrom the remaining characterizing features that are designated in thesubsidiary claims.

[0019] The invention will be elucidated in more detail below in examplesof embodiments on the basis of the associated drawings. The followingaspects are shown.

[0020]FIG. 1 shows a cross section through a refrigerant tube and

[0021]FIG. 2 shows a longitudinal section though a segment of arefrigerant tube.

[0022]FIG. 1 shows a refrigerant tube 10 in the form of a cross section.The refrigerant tube 10 comprises a casing, which is designated in itsentirety by 12, that encloses an inner zone 14. The casing 12 is formedfrom a flexible cord-like hollow object that encloses an inner zone 14that is preferably constructed in the form of a cylinder with a circularcross section. In accordance with further examples of embodiments, theinner zone 14 can also have a different shape, e.g. an oval or similarshape. The casing 12 is constructed in a multi-layer manner. A middlelayer 20 is arranged around an inner layer 18, whereby an outer layer 22adjoins the middle layer. A reinforcing layer 24 is arranged between themiddle layer 20 and the outer layer 22. The layers 18, 20 and 22 of thecasing 12 comprise a polymeric material, for example. The reinforcinglayer 24 comprises a flexible fabric-reinforced layer, for example.

[0023] A barrier layer 26 is applied to an outer casing surface 16 ofthe inner layer 18. The barrier layer 26 is connected over its entiresurface and in a non-positive [adherent] manner to the casing surface16. The barrier layer 26 can be achieved in such a way, for example,that the inner layer 18 is produced first, and then the barrier layer 26is applied thereto, and subsequent layer assembly takes place on thebarrier layer 26.

[0024] The barrier layer 26 comprises a metal or a synthetic material,for example. The material of the barrier layer 26 is optimized in termsof the refrigerant that is to be transported through the inner zone 14of the refrigerant tube 10. Consideration can be given to e.g. to carbondioxide CO₂ as the refrigerant.

[0025] The casing surface 16 can be roughened in order to achieve a highstrength of adhesion between the barrier layer 26 and the inner layer18. This can take place e.g. physically, via the mechanical action of asuitable device, or chemically via alkalis, acids or similar substances.Adherent bonding to the barrier layer 26 is improved as a result of theroughness that is thereby achieved. In accordance with a further exampleof an embodiment, a bonding agent can be applied between the barrierlayer 26 and the layer 18 and/or the layer 20. The casing surface 16 canalso be polarized or activated in order to increase the strength ofadhesion.

[0026]FIG. 2 shows a schematic longitudinal section through therefrigerant tube 10. Parts that are identical to those in FIG. 1 areprovided with identical reference numbers and are not elucidated asecond time. For reasons of obtaining a good overview, the inner layer18 is not illustrated in FIG. 2 so that the barrier layer 16 is seen, asit were, in the cut open hollow zone 14. This [barrier layer] is, assuch, concealed by the inner layer (indicated on the left in FIG. 2). Afurther variant of an embodiment will be illustrated by means of thelongitudinal section, whereby the barrier layer 26 comprises individualsub-elements 30 that lie adjacent to the casing surface in a scale-likemanner. The casing surface 16 can, in turn, be mechanically and/orchemically roughened as in the case of the example of an embodiment thathas already been discussed in connection with FIG. 1. Moreover, anadditional bonding agent can be provided that is arranged between theinner layer and the barrier layer 26 and/or the middle layer 20 and thebarrier layer 26. FIG. 2 indicates, by means of the arrow 32, thehypothetical direction of transportation of a refrigerant through theinner zone 14. The scale-like arrangement, which is preferably provided,for the sub-elements 30 of the barrier layer 26 can take place in such away that these overlap both in the transportation direction 32 and alsocoaxially relative to the central axis 34 (in accordance with a furthervariant of an embodiment, overlapping can be dispensed with) (FIG. 1).As a result of the scale-like arrangement of the barrier layer 26, theflexibility of the refrigerant tube 10 is modified only insignificantlyby the introduction of the barrier layer 26. The sub-elements 30, whichare arranged in a scale-like manner, can follow [accommodate], with noproblem, stress due to the bending of the casing 12. The bending of thecasing 12 can be followed [accommodated] in all spatial directions bythe barrier layer 26 because of the overlapping of the sub-elements 30in the transportation direction 32 and/or in the coaxial directionrelative to the longitudinal axis 34.

[0027] It will be clear, in an overall way, that a refrigerant can betransported as a result of the integration of the barrier layer 26 intothe casing 12, whereby the volatile components of the refrigerant areunable to diffuse through the casing 12. Because of the barrier layer26, this [casing] acquires an extremely low permeability for themolecules of the refrigerant that it is to be transported. On the otherhand, the diffusion of molecules in the opposite direction and into theinner zone 14 is also prevented by the barrier layer 26.

1. Flexible cord-like hollow object with an inner zone, which isenclosed by a casing, for the transportation of media, whereby a barrierlayer (26), which is impermeable to the volatile molecules of the mediumthat is to be transported, is integrated into the casing (12),characterized by the feature that the barrier layer (26) comprisessub-elements (30) that are arranged in a scale-like manner.
 2. Flexiblecord-like hollow object in accordance with claim 1, characterized by thefeature that the sub-elements (30) overlap in the transportationdirection (32) of the medium.
 3. Flexible cord-like hollow object inaccordance with one of the preceding claims, characterized by thefeature that the sub-elements (30) overlap coaxially relative to thelongitudinal axis (34) of the casing (12).
 4. Flexible cord-like hollowobject in accordance with claim 1, characterized by the feature that thebarrier layer (26) is arranged on the outer metal surface (16) of aninner layer (18) of the casing.
 5. Flexible cord-like hollow object inaccordance with one of the preceding claims, characterized by thefeature that the barrier layer (26) comprises metal.
 6. Flexiblecord-like hollow object in accordance with one of the preceding claims,characterized by the feature that the barrier layer (26) comprisessynthetic material.
 7. Flexible cord-like hollow object in accordancewith one of the preceding claims, characterized by the feature that thebarrier layer (26) is connected in a non-positive [adherent] manner tothe casing surface (16).
 8. Flexible cord-like hollow object inaccordance with one of the preceding claims, characterized by thefeature that the casing surface (16) is treated physically and/orchemically in order to increase the strength of adhesion of the barrierlayer (26).
 9. Flexible cord-like hollow object in accordance with oneof the preceding claims, characterized by the feature that the casingsurface (16) is roughened.
 10. Flexible cord-like hollow object inaccordance with one of the preceding claims, characterized by thefeature that the material of the casing (12) is polarized at least inthe surface region of the casing surface (16).
 11. Flexible cord-likehollow object in accordance with one of the preceding claims,characterized by the feature that the material of the casing (12) isactivated at least in the surface region of the casing surface (16). 12.Flexible cord-like hollow object in accordance with one of the precedingclaims, characterized by the feature that a bonding agent is arrangedbetween the barrier layer (26) and the casing surface (16).
 13. Flexiblecord-like hollow object in accordance with one of the preceding claims,characterized by the feature that the casing (12) comprises at least onelayer (18, 20, 22) that comprises a polymeric material.
 14. Flexiblecord-like hollow object in accordance with one of the preceding claims,characterized by the feature that the casing (12) has a triple layerstructure.
 15. Flexible cord-like hollow object in accordance with oneof the preceding claims, characterized by the feature that a reinforcinglayer (24) is arranged between at least two layers (20, 22) of thecasing (12).
 16. Use of a flexible cord-like hollow object in accordancewith one of the claims 1 through 15 for the transportation of arefrigerant, especially carbon dioxide CO₂.
 17. Use of a flexiblecord-like hollow object in accordance with one of the claims 1 through15 in technical refrigeration units in motor vehicles.